Assuming that no persons share the same birthdate, this is how we might code it in subquery:

select m.*,
ElderBirthDate =
(select top 1 x.BirthDate
from Member x
where x.BirthDate < m.BirthDate
order by x.BirthDate desc)
from Member m
order by m.BirthDate;

Now, some nasty users requested for more information, she wanted to see that elder person's Firstname too; as a good developer you are, of course you will comply. Here's your new query:

select m.*,
ElderBirthDate =
(select top 1 x.BirthDate
from Member x
where x.BirthDate < m.BirthDate
order by x.BirthDate desc),
ElderFirstname =
(select top 1 x.Firstname
from Member x
where x.BirthDate < m.BirthDate
order by x.BirthDate desc)
from Member m
order by m.BirthDate

Then a day after, she requested to add the Lastname, she deemed that it is nice to have that information on the report too. Things are getting hairy isn't it? We are violating DRY principle, if we are using subquery approach.

Enter OUTER APPLY, this neat technology is ought to be present in all RDBMS, unfortunately(if you expect that it is available on all RDBMS at the time of this writing) this is available on SQL Server only:

select m.*, elder.*
from Member m
outer apply
(
select top 1 ElderBirthDate = x.BirthDate
from Member x
where x.BirthDate < m.BirthDate
order by x.BirthDate desc
) as elder
order by m.BirthDate

Compared to subquery, at first glance it doesn't seem to add much in terms of value; but where it shines is it can pick up all the columns on the matched condition. Now back to the requested new column on report by our dear user, we can neatly add those column(s) if we are using OUTER APPLY instead:

select m.*, elder.*
from Member m
outer apply
(
select top 1 ElderBirthDate = x.BirthDate, ElderFirstname = x.Firstname
from Member x
where x.BirthDate < m.BirthDate
order by x.BirthDate desc
) as elder
order by m.BirthDate

Not only there is less friction on modifying our query based on user's requests when we uses OUTER APPLY, our OUTER APPLY query scales nicely too:

Now there's a new request in town to display the person's two immediate elder brothers; if we are using subquery, we might cringe at the thought of rewriting our query just to facilitate such whimsical requirement. But hey, we are using OUTER APPLY, you can laugh in triumph rather than quivering in pain, just modify the TOP 1 to TOP 2 to support that requirement. Convenient isn't it?